An N-vinylamide polymer has advantageous properties such as biocompatibility, safety, and hydrophilicity and functions as a thickening agent, a flocculant and the like, and thus is useful for production raw materials of pressure sensitive adhesives, coating materials, dispersants, ink, electronic parts and the like other than pharmaceutical products and cosmetics, additives for food and the like. To make such an N-vinylamide polymer suitably used for these various applications, improvements in qualities, abilities, and safety are important.
Conventionally, in the case of producing, for example, polyvinylpyrrolidone, to lower remaining N-vinylpyrrolidone (NVP), a method, in which NVP is hydrolyzed after the polymerization, has been known. In this method, hydrolysis products such as 2-pyrrolidone (2-py), acetaldehyde and the like are produced and sometimes cause toxicity, malodor, and coloration. Further, a method of decreasing the NVP by adding an initiator afterward during polymerization has also been known, however in this case, hydrolysis may be promoted during polymerization to produce 2-py and the like. Also, when polymerization is carried out in a solvent, it is possible to suppress hydrolysis of monomers, but K-value decrease. Therefore elimination of the problems are needed.
With respect to production methods of conventional N-vinylamide polymer, the following methods have been disclosed.
That is, a method of producing polyvinylpyrrolidone (PVP) with a high K-value while suppressing generation of hydrazine, an impurity, by using an azo initiator (e.g. reference to Japanese Kokai Publication Hei 9-110912 (page 2)). In such a production method, no description of the amount of 2-pyrrolidone, an impurity, but when polymerization is carried out according to the disclosed conditions, at least 0.05% of 2-pyrrolidone may be produced during polymerization. Also, in many cases, commercialized polyvinylpyrrolidone having K-value of 90 contains 0.1% or more of 2-pyrrolidone.
With respect to the N-vinylamide polymer such as polyvinylpyrrolidone, generally, its property is expressed with the K-value. The K-value means a value calculated according to Fickencher's formula from a relative viscosity of an aqueous solution of 1% by weight of the N-vinylamide polymer measured by a capillary viscometer and is supposed to have a correlation with the molecular weight of the polymer. In the case of the N-vinylamide polymer, the polymer has amido bonds and the bonds are adsorbed on a column of gel permeation chromatography (GPC) to disable precise molecular weight analysis and therefore, the K-value is employed instead.
As a production method of vinylpyrrolidone polymers, continuous polymerization of vinylpyrrolidone in an organic solvent under pressure of 1 Barr or higher and a high temperature in the presence of a radical polymerization initiator is disclosed (e.g. reference to Japanese Kokai Publication Sho-51-82387 (page 1–2)). In this production method, there is a description that polymers of N-vinylpyrrolidone having K-value of 10 to 35 with little amount of impurities are produced by polymerizing N-vinylpyrrolidon in an organic solvent under pressure.
As a production method of N-vinyl-2-pyrrolidone polymers, production of the polymers with K-value of 10 to 100 by adding di(tertiary butyl)peroxide to an aqueous solution of 10 to 80% by weight of N-vinyl-2-pyrrolidone for polymerization and adding an adjustment agent during the polymerization is disclosed (e.g. reference to Japanese Kokai Publication Sho-63-156810 (page 2)). In this production method, there is a description that the mixture is stirred and simultaneously the polymerization is carried out and that the obtained polymers contain 50% by weight or more of polymerized N-vinyl-2-pyrrolidone and are clearly dissolved in water and an organic solvent, and that the polymers are free from hydrazine. Further, no description regarding the amount of 2-pyrrolidone, an impurity, is given, but when polymerization is carried out according to the disclosed conditions, at least 0.1% of 2-pyrrolidone may be produced during the polymerization.
As a production method of vinylpyrrolidone polymers, production of the polymers by adding a water-soluble organic peroxide and a sulfite salt to an aqueous solution of vinylpyrrolidone is disclosed (e.g. reference to Japanese Kokai Publication 2002-69115 (pages 2, and 4 to 6)). However, in this production method, the addition amount of sodium sulfite is high and the vinylpyrrolidone polymer obtained may contain approximately 0.1% or more of sodium as an ash component relative to the polymer.
Accordingly, the production method still has a room for contrivance to improve and to produce the vinylpyrrolidone polymer with lesser contents of impurities such as 2-pyrrolidone and ash components and higher K-value.
Further, with respect to a water-soluble polymer production method, it is disclosed that an aqueous solution containing at least 50% by weight of a monomer is irradiated with radiation beam in form of a thin film having a thickness of 2 cm or thinner on an underlay placed under a radiation beam source (e.g. reference to Japanese Kokai Publication Sho-46-2094 (pages 1, 2 and 5)). In this production method, it is described that the reaction temperature is 5 to 100° C. and the reaction is preferably carried out without supplying heat. Also, in the Example, it is described that N-vinylpyrrolidone is used as the monomer and benzoin isopropyl ether is used as a photopolymerization initiator. However, in such a production method, coloration of the obtained polymer or coloration over time may not be avoided.
With respect to another water-soluble polymer production method, it is disclosed that an acrylic polymer is obtained by supplying an aqueous monomer solution containing a cationic vinyl monomer and a nonionic surfactant in 3 to 10 mm thickness on a movable belt and radiating UV rays to the solution (e.g. reference to Japanese Kokai Publication Sho-61-155405 (pages 1 and 2)).
In this production method, the surfactant is added to the aqueous monomer solution so as to suppress gelation of the acrylic polymer and at the same time provide the polymer with a high molecular weight.
Further, with respect to a water-absorptive resin production method, it is disclosed that the obtained water-containing gel-phase polymer is kept at a temperature lower than the peak temperature by at least 10° C. for not shorter than 30 minutes in the static aqueous solution polymerization of the monomer component (e.g. reference to Japanese Kokai Publication 2000-34307 (pages 2 and 7 to 10)). However, in this production method, the Example has a description that polymerization is carried out using acrylic acid and its salt as main components of monomer components by a movable type belt polymerization apparatus. Also, it is described that the monomer concentration is preferably 45% or lower.
With respect to a radical polymerization method of an unsaturated water-soluble monomer, it is disclosed that in the case of carrying out radical polymerization of an unsaturated water-soluble monomer or the like in a layer having a thickness of 2 to 100 mm by using UV rays, an anthraquinone derivative and dissolved chloride ion are added to carry out the polymerization (e.g. reference to Japanese Kokai Publication Sho-52-47084 (pages 1, 3 and 4)). In this production method, it is also described that (meth)acrylamide in 50% by weight or more is preferably used and also vinylpyrrolidone is preferable to be used. Further, description says that the polymerization temperature is 0 to 100° C. and the obtained polymer may be used for a caking additive, a finishing agent, a glue or the like.
With respect to a gel composition suitable for a high polymer solid electrolyte, it is described that the gel composition contains a cross-linked polymer obtained by polymerization of monomer components comprising cyclic N-vinyllactam and an organic solvent (e.g. reference to Japanese Kokai Publication Hei-10-101886 (pages 2, 5 and 7)), and that the cross-linked polymer is obtained by static polymerization on a belt or a tray. Also, the Example has a description that using an azo initiator as a polymerization initiator and N-vinyl-2-pyrrolidone in a monomer concentration of 30% by weight as the cyclic N-vinyllactam, reaction is carried out at 50° C.
Further, with respect to a polymer suitable for a thickener and a soil amendment agent, a copolymer of N-vinylpyrrolidone and acrylic acid is described (e.g. reference to Japanese Kokai Publication 2001-48938 (pages 2 and 5)). The Example has a description that using an azo initiator as a polymerization initiator and N-vinyl-2-pyrrolidone and sodium acrylate as monomer components, reaction is carried out at 45 to 70° C. reaction temperature and 35% monomer concentration.
However, in the above-mentioned production method, there still remain problems to be solved that production of 2-pyrrolidone and ash components cannot be suppressed all together to sufficiently low, or the obtained polymers are colored.
With respect to a conventional N-vinylamide polymer production method, a method of removing vinylpyrrolidone from a vinylpyrrolidone polymer by treating an aqueous or alcohol solution of the vinylpyrrolidone polymer with an adsorbent is disclosed (e.g. reference to Japanese Kokai Publication Sho-63-68609 (page 1)). However, the method of using an adsorbent requires treatment in solution state and thus the solution is limited in relation to the viscosity and it is supposed that 2-pyrrolidone, a hydrolysis product, may not be removed sufficiently.
Also, with respect to a production method of a polymer obtained by polymerizing and introducing N-vinylpyrrolidone, it is disclosed that a contaminant with a low molecular weight is separated from a polymer solution at 20 to 100° C. and 1 to 80 Barr using an ultrafilter (e.g. reference to Japanese Kokai Publication Hei-5-239118 (pages 2 and 3 to 6)). In such a method, the treatment in solution state is also required and in the Example, there is only a description of decrease ratio of 2-pyrrolidone before and after the treatment, but it is supposed that generally approximately 1% of contaminant is generated on completion of polymerization and the contaminant may remain approximately 500 ppm in the polymer. Further, since polymerization is carried out using hydrogen peroxide, the obtained polymer may be colorized.
Such refining methods by adsorbent treatment and ultrafiltration and the like are carried out in solution state, resulting in the lower quantities of the polymers treated per unit time. Further, the viscosities of the solutions treated are limited, and particularly in the case of an N-vinylamide polymer with a high K-value, the treatment has to be carried out at a low solution concentration resulting in further decrease of the productivity and thus these methods are not practical. Accordingly, there was a room for contrivance to solve these inconveniences, to sufficiently improve the productivity, and to produce the N-vinylamide polymer suitable for uses such as cosmetics and pharmaceutical products.
With respect to a method of producing a hydrophilic polymer with a low remaining monomer content, it is disclosed that a water-containing gel-phase polymer is dried by being brought into contact with a gas containing at least steam and having a dew point of 50 to 100° C. at a temperature of 80 to 250° C. (e.g. reference to Japanese Kokai Publication Sho-64-26604 (pages 1 to 2, 4 and 6 to 12)).
In the Example, there is a description that a gel-phase polymer with a water content of 25% or higher is produced from an acrylic acid salt and acrylamide as main components of monomer and dried until the solid concentration reaches to 96% at highest and that the remaining monomer concentration in the obtained hydrophilic polymer is 20 to 2200 ppm.
With respect to a method for separating a trace amount of vinyl chloride monomer from a vinyl chloride resin powder, it is disclosed that the vinyl chloride resin powder wetted with a water-based solvent is heated and that the vinyl chloride monomer existing in the water-based solvent is evaporated and separated in a normal or reduced pressure (e.g. reference to Japanese Kokai Publication Sho-51-126284 (pages 1 to 3)).
These methods have no description regarding production of the N-vinylamide polymer used for cosmetics and pharmaceutical products and there was a room for contrivance to improve a production suitably employed for such polymer production.